Tuning section



March 21, 1951 L. A. BROCKWELL ETAL 2,976,500

TUNING SECTION 2 Sheets-Sheet 1 Filed Oct. 29, 1957 z/v vE/vraes LL UYDA.EHDBKWELL i3 JusEPH J.MATTA BY Arron/5r March 1961 L. A. BROCKWELLEI'AL 2,976,500

TUNING SECTION Filed Oct. 29, 1957 2 Sheets-Sheet 2 INVENTORS LLOYD AbauBKWE LL fiJu SE PI-LJ. MATTA Unit TUNING SECTION Filed Oct. 29, 1957,Ser. No. 694,696

4 Claims. ((31. 333-11) The invention relates to a tuning section for awaveguide or a cavity resonator, and has for an object to provide atuning section that permits a probe-like element to be readily placed inany one of a very large number of positions in the resonator or thewaveguide with a minimum of radio frequency leakage therefrom.

The invention is intended to be used with a cavity resonator or with awaveguide having at least one fiat wall having a circular opening. Afirst circular plate that has a diameter substantially equal to thediameter of the circular opening is rotatably fitted in the circularopening. The first plate also has a circular opening, this circularopening encompassing an area which includes the center of the firstplate and being eccentrically positioned in the first plate. A secondcircular plate that has a diameter substantially equal to the diameterof the circular opening in the first plate is rotatably fitted in thecircular opening in the first plate. A probelike coupling or tuningelement is positioned at a point .on the second plate that coincideswith the center of the first plate for one position of rotation of thesecond plate. By a proper rotation of the two plates, it is possible toposition the probe-like element at any point corresponding to any one ofan infinite number of positions of the plates within the circumferenceof the first plate. The plates may be rotatably fastened in theirrespective openings so that substantially no discontinuity is presentedin the waveguide wall. Thus leakage of radiofrequency energy from thecavity resonator or the waveguide is reduced to a minimum.

The invention is explained in detail in connection with the accompanyingdrawing, in which:

Figure 1 shows a plan view of a rectangular cavity resonator or awaveguide having a tuning section in accordance with the invention;

Figure 2 is a transverse cross-sectional view taken along the lines 22in Figure 1;

Figure 3 is an enlarged view of a portion of Figure 2 that shows thedetails of mounting the plates of the tuning section in their respectiveopenings; and

Figure 4 shows a hybrid junction utilizing a tuning section inaccordance with the invention.

The invention is intended to be used with a cavity resonator or with awaveguide having at least one fiat metallic wall, such as therectangular structure shown in Figures 1 and 2. A circular opening ismade in one metal wall 12 of the resonator or waveguide 10, it beingpreferred that this circular opening be symmetrically positioned in thetransverse direction of the wall 12. A first circular electricallyconductive metal plate 14, having a diameter substantially equal to thediameter of the opening in the wall 12, is positioned in the opening inthe Wall 12. The first plate 14 has a circular opening, the area ofwhich includes the center of the first plate 14. This last circularopening is eccentrically positioned in the first plate 14. A secondelectrically conductive circular metal plate 16, having a diametersubstantially equal to the diameter of the opening in the first plate14,

2,976,500 Patented Mar. 21, 1961 ice is positioned in the. opening inthe first plate 14. A probe-like element, such as the inner conductor ofa coaxial transmission line 20, is fastened to the second plate 16 at apoint that coincides with the center of the first plate 14for oneposition of rotation of the second plate 1.6. The transmission line 20has an outer conductorZZ-which is. connected to thesecond plate 16, andan inner conductor 24 which passes through an opening in the. secondplate 16 at the point already mentioned sothat the inner conductor 24extends into the interior of the waveguide 10. While Figures 1 and 2show a coaxial transmission line 20, it will be appreciated that anyprobe-like element, such as an inductive or capacitive probe (dependingupon the length of theprobe), can be fastened to the second plate 16insteadof the coaxial transmission line 20. The exact dimensions of theprobe and its shape are determinable from electrical considerations.

The first and second plates 14, 16 are preferably made of the'sameelectrically conductive material as the st-ruc ture 10, and preferablyhave the same thickness as the wall 12 so as to introduce a minimum ofdiscontinuity to radio frequency energy propagated inand through thewaveguide 10. The first and second plates 14, 16 are designed to fit intheir respective openings with just enough clearance so that the plates14, 16 may be rotated and still present a substantially smooth andunbroken surface to the wall- 12 of the waveguide 10. It will be seenthat a proper combination of positions of either or both of the twoplates 14, 16 makes it possible to position the coaxial transmissionline 20 at any point Within the circumference of an imaginary circlealmost as large as the first plate 1 4. Thus, the coaxial transmissionline 20 may be coupled :to the interior of the waveguide 10 at anydesired point within this imaginary circle without introducing adiscontinuity in the waveguide 10, such as would be introduced by anelongated slot. If the plates 14, 16 are snugly fitted in theirrespective openings, a minimum of radio frequency energy will leakthrough the small clearance space between the plates 14, 16 and theiropenings. V

Figure 3 is an enlarged view of a portion of Figure 2, and shows one wayin which the plates 14, 16 may be mounted in their respective openingsso as to provide a minimum of discontinuity and leakage in the waveguide10. Each of the openings is provided with a small shoulder-like rim orflange 30 that'extends around each of the circumferences of theopenings. The plates 14, 16 are provided with a corresponding depressionor groove so that each of the plates 14, 16 fits in its respectiveopening. When the plates 14, 16 are placed in their respective openings,they rest on the shoulders of their respective rims or flanges 30. Eachof the plates 14, 16 may then be held in position by circular rings orseals 34 which cover the outer junction of the plates 14, 16 and theirrespective openings. Thus, an integral, electrically conductive junctionmay be provided for the plates 14, 16 and their openings.

Figure4 shows a hybrid junction 40 utilizing a tuning section inaccordance with the invention. Hybrid junctions are known in the art,and an explanation of them may be found beginning on page 339 ofWaveguide Transmission by Southwonth, 3rd printing, 1956, D. VanNostrand Company, Incorporated. Generally, a hybrid junction may have adiscontinuity due to mismatch of loads. These discontinuities areobviated by means of an appropriate compensating susceptance usually inthe form of one or more appropriately positioned rods or probe-likeelements positioned within the junction. These rods act either as ashunt inductance or as a shunt capacitance. While two rods or probe-likeelements are generally needed, only one rod 42 is shown 'twotuningsections.

in Figure 4 in the interests of clarity. As mentioned by Southworth inthe above reference, the exact position of the rods is usually arrivedat by empirical means, or by experimentation. If the two plates of thetuning section described in connection with Figures 1, 2, and 3 areplaced in an appropriate wall of the hybrid section 40, and the rod 42fastened to one plate, the location of the rod 42 may be varied. Thus,the tuning section of the invention provides a simple, yet efiectivemeans for positioning the rod within the hybrid section 40 in the bestlocation after the hybrid section 40 is constructed and connected intooperating apparatus.

While the tuning sections of the invention have been described inconnection with probe-like elements which are fastened to a tuningsection at only one end, it will be appreciated that two tuningsections, one being positioned in one wall of a waveguide and the otherbeing positioned at a corresponding position in an opposite wall, can beused with a probe connected between the Such an arrangement requiresthat the two tuning sections be rotated simultaneously and in thecorresponding manner and directions.

The term probe, as used in the specification and claims, is deemed toinclude any rod-like element or wire, an electrically conductive loop,or any conductive structure which can be used to afiect radio frequencyenergy in a waveguide or cavity structure or to couple energy to or fromsuch a waveguide or cavity structure.

' The invention claimed is: V

1. A tuning section for a cavity resonator or a waveguide havingat'least one substantially fiat wall, said wall having a circularopening therein, comprising a first circular plate having a diametersubstantially equal to the diameter of said circular opening and beingadapted to rotatably fit in said circular opening, said first platehaving a circular opening eccentrically. positioned there in, a secondcircular plate having a diameter substantially equal to the diameter ofsaid circular opening in said first plate and being adapted to rotatablyfit in said circular opening in said first plate, and means forattaching a probe-like element to-said second plate so as to extend intothe interior of said waveguide.

2. A tuning section for a cavity resonator or a waveguide having atleast one substantially fiat wall, said wall having a circular openingtherein, comprising a first circular plate having a diametersubstantially equal to the diameter of said circular opening and beingadapted to rotatably fit in said circular opening, saidfirst platehaving a circular opening therein eccentrically positioned e in saidfirst plate and the area of which includes the center of said firstplate, a second circular plate having a diametersubstantially equal tothe diameter of said circular opening in said first plate and beingadapted to rotatably fit in said circular opening in said first plate, atuning element fastened to said second'plate so as-to extend into theinterior of said waveguide, said tuning element being positioned at apoint on said second plate that coincides with the center of said firstplate for one position of rotation of said second plate, and means forfastening said second plate in said opening in said first plate so thatsaid second plate may rotate therein.

3. A tuning section, comprising a rectangular waveguide, one wall ofsaid waveguide having a circular opening symmetrically positionedtherein in the transverse direction, a first circular plate having adiameter substantially equal to the diameter of said circular openingand being adapted to rotatably fit in said circular opening, said firstplate having a circular opening therein eccentrically positioned in saidfirst plate and the area of which includes the center of said firstplate, means for fastening said first plate in said opening in said wallso that said first plate may rotate therein, a second circular platehaving a diameter substantially equalto the diameter of said circularopening in said first plate and being adapted to rotatably fit in saidcircular opening in said first plate, a probe fastened to said secondplate and extending into the interior of said waveguide, said probebeing positioned at a point on said second plate that coincides with thecenter of said first plate for one position of rotation of said secondplate, and means for fastening said second plate in said opening in saidfirst plate so that said second plate may rotate therein.

4. In combination with a hybrid junction, said hybrid junotioncomprising a plurality of waveguides which are intercoupled at a commonpoint, and said junction having at least one substantially fiat wallhaving acirc'ular opening therein, a first circularplate havinga-diameter substantially equal to the diameter of said circular openingand being adapted to rota-tably fit in said circular opening, said firstplate having a circular opening eccentrically positioned therein, thearea of which includes the center of said first plate, a second circularplate having a diameter substantially equal to the diameter of saidcircular opening in said first plate and being adapted to rotatably fitin said circular opening in said first plate, and a probe-like elementattached to said second plate so as to extend into the interior of saidhybrid junction, said probe-like element being positioned at a point onsaid second plate that coincides with the center of said first plate forone position of rotation of said second plate;

References Cited in the file of this patent v FOREIGN PATENTS V v I157,564 Australia July 8, 1954

